As both our societies and our workplaces become more diverse, it's more common to find different languages spoken on our teams. Here are some points to bear in mind:
Communicate really important information both orally and in writing. Often, workers for whom English is a second language are more skilled in reading and writing the language than in conversation.
Pay attention to your nonverbal signals. Your tone of voice or gestures may have different--and undesirable--meanings in your workers' native cultures. For example, pointing directly at someone's face is the height of rudeness in some cultures.
Along the same lines, be extremely careful about trying to translate information unless you're fluent in the workers' native language. A real-life example: A California firm gave Spanish-speaking workers a translated test to measure their understanding of forklift safety. On the test, the words "honk your horn" were rendered in Spanish as vulgar slang for a sexual act.
Remember that communication is a two-way street. Listen to all your workers have to say before you assume that they haven't understood you. You may find that, actually, you haven't understood them.
Also remember that, even though non-native English speakers may be shy or awkward at communicating, they probably aren't shy or awkward in general. It's likely that they'll be quite assertive and motivated, even if that's not reflected in their language skills.